On the basis of extensive experimental studies of Pb${}_{1-x}$Ba${}_x$(Fe${}_{1/2}$Nb${}_{1/2}$)O${}_3$ (PFN-BFN) and Pb(Fe${}_{1/2}$Nb${}_{1/2}$)${}_{1-x}$Ti${}_x$O${}_3$ (PFN-PT) single crystals by several experimental methods, we have proposed phase diagrams describing the magnetic properties of these solid solutions. The comprehensive consideration of the magnetic properties of the PFN-based solid solutions has shown that these phase diagrams can be explained on the basis of a model suggested earlier for pure PFN [Phys. Rev. Lett. 105, 257202 (2010)]. This model assumes the coexistence in the crystal lattice of the long-range antiferromagnetic (AFM) cluster, which defines the Néel order parameter, with the finite-size mixed ferromagnetic-AFM clusters, responsible for the spin-glass order parameter. We state that one of these parameters, the Néel temperature, linearly decreases with the increasing dopant concentration and eventually disappears at some critical concentration as a result of the percolation phase transition. The other parameter survives until the maximal concentrations studied. We have also found a phase which can be related to the super-AFM order. These data can have important implications and provide the basis for the development of novel fundamental theory of multiferroics with the site, charge, and spin disorder.

• Received 22 November 2012

DOI:https://doi.org/10.1103/PhysRevB.87.064403